Things like this are usually a bit tricky. Here is such a trick:
In[49]:=
exp = -1-5*(3^x)+(31/63)*(2^(2+x))*(5^(1+x))-((53*(10^x))/63);
2^x Simplify[exp/2^x]
Out[50]=
-1 - 5*3^x + 9*10^x
Fred Simons
Eindhoven University of Technology